The invention relates to a valve control mechanism for intake and exhaust valves of internal combustion engines having at least one adjustment element with which the intake or exhaust valve is opened and closed.
In standard internal combustion engines, the control of the lifting movement of the intake and exhaust valves takes place through one of the crankshafts in a speed-ratio of 2:1 relative to the driven camshaft. The lifting curve of the valve is proportional to the curve of the cam for the entire sphere or reach of the performance graph and therewith unchangeable. The closing point of the intake valve is, conditional on the variable flow velocity in the exhaust pipe, not optimally situated. The intake valve""s opening point, likewise, can also not be optimally situated. The data for the best possible (ideal) operating capacity of the combustion chamber at a high number of revolutions and of the cylinder-exhaust contents at a low number of revolutions and in idle are diametrically opposite. The opening point for the exhaust source is usually selected so that the exhaust release is minimized and the gas is in the position to perform the maximum amount of work.
Through avoidance of the aforementioned adjustments, there are always compromises, valve control mechanisms are developed, in order to be able to affect and change control-reaction time, stroke response of the intake/exhaust valves as a function of the engine speed, which load and other limiting qualities control and change. The operation of the valve lift can be affected or changed therewith through variation of the phase-relationship of the valve lift or the valve-opening time. Such measures can be used singly or in combination, on the one hand, in order to reduce fuel consumption and emissions of spark-ignition engines, while on the other hand, to improve the flow of the torque and to achieve the maximum power or output. A further advantage is the possibility that the sucked-in air mass can be affected by changing the cross-section of the valve opening, thereby making possible a choke-free load control without a throttle valve or flap.
Through multi-valve technology, such wiring can be undertaken, that the sucked-in load flows only over an intake valve, by which the air mass is affected. A cylinder shutoff, through the control of the intake/exhaust valve, likewise can be involved, whereby the fired cylinders can work most efficiently through the masking of the injection and combustion air. With modern engine electronics, the cylinder shutoff can be cyclically (selectively changed, in order to avoid the cooling-off of the cylinder wall.
The possibilities described above for controlling and altering of parameters are grouped together under the concept xe2x80x9cvariable valve control mechanisms.xe2x80x9d The manner of valve operation varies between direct and indirect operating systems.
With indirect operating systems, two solutions are known, namely the use of a variable camshaft or a variable intermediate element. With direct operating systems, basically three possibilities are known, which result in either a hydraulic, pneumatic or electric operation of the valve. A camshaft is not used in this situation.
In the hydraulic system, energy is saved, similar to a so-called Common Rail System and through fast-acting magnet valves or servo valves of the set piston surfaces, the energy is fed or discharged, by which the intake/exhaust valves are operated. Such systems are known for their use in long-running diesel engines.
The invention addresses the underlying problem of developing the type of valve control mechanism which operates simply and reliably at high switching frequencies, instead of an expensive servo valve, so that the valve control mechanism is also useful for high rotary internal combustion engines.
This problem is resolved by the type of valve mechanism with the specific charateristics of the invention namely, at least one piezo element; at least one valve element that is operated by said at least one piezo element; and at least one adjustment piston, wherein inflow and outflow of a pressure medium to the at least one adjustment piston is controlled by the at least one valve element, and wherein the at least one adjustment piston is moveable by the pressure medium, against the counter pressure for opening an intake or exhaust valve.
With the valve control mechanism which is the subject of this invention, a piezo electric actor is employed as an adjustment element. With this, a lightweight valve element is operated, which controls the inflow and outflow of the pressure medium to and from the adjustment piston, by whose lift the intake and exhaust valves of the internal combustion engine are opened and closed. Piezo electric actors convert electric voltage directly into movement and energy. The conversion of the electric input quantity into a mechanical output quantity occurs extremely quickly. By way of example, an adjustment lift of 40 xcexcm (0.04 mm) can occur at a regulating time of 50 xcexcs (0.00005 sec). The dissociation of the adjustment path, or movement, is possible in smaller electric currents of nanometers (0.0001 mm). Adjustment force is reached in kilo-newtons, that is to say, it acts as a correcting element with very high mechanical rigidity.
In the high-dynamic area, on the one hand, the availability of the suitable energy amplification is an essential prerequisite, in order to synchronize the current-running and the reaction of the intake and exhaust valves. On the other hand, the flow-through cross-section of the seating valve has to be adequately large in dimension. This results in an advantageous development of the valve control mechanism of the present invention by increasing the lift in value, for which the available adjustment movement of the piezo electric transformer does not suffice. Therefore, an adjustment-movement enlarger, or increaser, is used, which advantageously works by the principles of levers and which can increase the useable adjustment movement or action of the valve element, for example, to a factor of xcexd=10.
With the valve control mechanism of the present invention, the opening and closing points of the intake and exhaust valves can be determined as required.